The invention relates to the field of so-called xe2x80x9crigidxe2x80x9d single row ball bearings.
Such bearings comprise an outer ring equipped with a toroidal raceway on its bore, an inner ring equipped with a toroidal raceway on its external surface, a row of balls arranged between the two raceways, in contact with said raceways, the profile of the raceways being symmetric with respect to a plane passing through the center of the balls, a cage in the form of an annular element with a certain number of cavities intended to house the balls and space them apart circumferentially in an appropriate way to avoid any imbalance when the bearing is running, and possibly sealing members in the form of seals or flanges arranged on one or both sides of the bearing so as to prevent any ingress of contaminants from the outside and prevent any leak of lubricant to the outside of the bearing.
Such bearings are known and used in many applications.
In order to make for easier sourcing and interchangeability of such bearings from one manufacturer to another, the dimensions relating to the parameters defining the size and fitting of these bearings have been standardized to give so-called xe2x80x9cISOxe2x80x9d series of bearings.
These series call upon basic four-figure designations (6000, 6200, 6300 series) common to all bearing manufacturers, nominal size dimensions (D=outside diameter, d=bore and B=width) identical across all manufacturers corresponding to each basic designation.
The user thus has standard ranges of bearings available which makes his choice easier and ensures that the bearings will be interchangeable.
The functional life of a bearing is not tied only to the basic bearing material but depends also on the lubricant used and on the other elements which make up the bearing, such as the cage or the sealing members.
While conventional bearings in the ISO range are entirely satisfactory in most applications, failures through lack of lubrication or through excessively short grease life have been observed in certain instances.
These are mainly applications relating to the field of electric motors, in which the bearing is not very heavily loaded with respect to its load-bearing capacity but is running at high speed and at relatively high temperatures.
In this type of application, it is usually the qualitative or quantitative degradation of the grease, rather than the load-bearing capacity of the bearing which governs the bearing life. Attempts at preventing failures may be made by using, for example, so-called xe2x80x9copenxe2x80x9d (flangeless and seal-less) bearings lubricated with grease and which are periodically repacked, which is expensive.
One of the objects of the invention is to propose a new range of bearings better suited to these applications, having overall size dimensions identical to those of the conventional ISO bearings, but with internal construction features that make it possible to guarantee a high service life by virtue of excellent lubrication with grease held in by effective sealing.
The ball bearing device according to the invention is of the type comprising an outer ring equipped with an outer surface and with a bore on which a toroidal inner raceway is formed, an inner ring equipped with a bore and with a cylindrical outer surface on which a toroidal outer raceway is formed, a row of balls arranged between the two raceways, and a cage capable of keeping a uniform circumferential spacing between the balls. The ratio between the radial thickness of the outer ring taken between the bottom of the inner raceway and the outer surface of the outer ring, and the diameter of the balls is between 0.4 and 0.7. The ratio between the radial thickness of the outer ring taken between the bottom of the inner raceway and the outer surface of the outer ring, and the radial thickness of the inner ring taken between the bottom of the outer raceway and the bore of the inner ring is between 1.1 and 1.6.
In other words, by comparison with conventional ISO bearings, the diameter of the balls is smaller, the radial thickness of the outer ring is greater at the bottom of the raceway and the radial thickness of the inner ring at the bottom of the raceway is kept more or less the same.
Advantageously, the ratio between the radial thickness of the outer ring taken between the bottom of the inner raceway and the outer surface of the outer ring, and the outside diameter of the bearing is between 0.045 and 0.08.
Advantageously, the ratio between the width of the rings and the diameter of the balls is between 1.3 and 2.2.
Advantageously, the ratio between the width of the rings and the radial thickness of the outer ring taken between the bottom of the inner raceway and the outer surface of the outer ring is between 2.5 and 4.2.
As a preference, the values of the outside diameter of the bearing, of the inside diameter of the bearing, and of the width of the bearing are identical to those of a conventional single row rigid ball bearing of the standardized ISO range.
In one embodiment of the invention, the ratio between the radial thickness of the outer ring taken between the bottom of the inner raceway and the outer surface of the outer ring, and the diameter of the balls is between 0.5 and 0.6, in that the ratio between the radial thickness of the outer ring taken between the bottom of the inner raceway and the outer surface of the outer ring, and the radial thickness of the inner ring taken between the bottom of the outer raceway and the bore of the inner ring is between 1.1 and 1.5, in that the ratio between the radial thickness of the outer ring taken between the bottom of the inner raceway and the outer surface of the outer ring, and the outside diameter of the bearing is between 0.045 and 0.06, in that the ratio between the width of the rings and the diameter of the balls is between 1.7 and 2.2, and in that the ratio between the width of the rings and the radial thickness of the outer ring taken between the bottom of the inner raceway and the outer surface of the outer ring is between 3 and 4.2, the values of the outside diameter of the bearing, of the bore of the bearing, and of the width of the bearing being identical to those of a conventional single row rigid ball bearing of the 6000 series of the standardized ISO range.
In another embodiment of the invention, the ratio between the radial thickness of the outer ring taken between the bottom of the inner raceway and the outer surface of the outer ring, and the diameter of the balls is between 0.4 and 0.7, in that the ratio between the radial thickness of the outer ring taken between the bottom of the inner raceway and the outer surface of the outer ring, and the radial thickness of the inner ring taken between the bottom of the outer raceway and the bore of the inner ring is between 1.2 and 1.6, in that the ratio between the radial thickness of the outer ring taken between the bottom of the inner raceway and the outer surface of the outer ring, and the outside diameter of the bearing is between 0.055 and 0.75, in that the ratio between the width of the rings and the diameter of the balls is between 1.5 and 1.9, and in that the ratio between the width of the rings and the radial thickness of the outer ring taken between the bottom of the inner raceway and the outer surface of the outer ring is between 2.5 and 4, the values of the outside diameter of the bearing, of the bore of the bearing, and of the width of the bearing being identical to those of a conventional single row rigid ball bearing of the 6200 series of the standardized ISO range.
In another embodiment of the invention, the ratio between the radial thickness of the outer ring taken between the bottom of the inner raceway and the outer surface of the outer ring, and the diameter of the balls is between 0.4 and 0.55, in that the ratio between the radial thickness of the outer ring taken between the bottom of the inner raceway and the outer surface of the outer ring, and the radial thickness of the inner ring taken between the bottom of the outer raceway and the bore of the inner ring is between 1.3 and 1.5, in that the ratio between the radial thickness of the outer ring taken between the bottom of the inner raceway and the outer surface of the outer ring, and the outside diameter of the bearing is between 0.065 and 0.08, in that the ratio between the width of the rings and the diameter of the balls is between 1.3 and 1.8, and in that the ratio between the width of the rings and the radial thickness of the outer ring taken between the bottom of the inner raceway and the outer surface of the outer ring is between 3 and 3.6, the values of the outside diameter of the bearing, of the bore of the bearing, and of the width of the bearing being identical to those of a conventional single row rigid ball bearing of the 6300 series of the standardized ISO range.
By virtue of the invention, in certain applications which would use open bearings lubricated by the circulation of oil, use may be made of bearings fitted with seals and greased for life.
Because of the reduction in the diameter of the balls, the volume not swept by the balls when the bearing is running is increased, and there is more space in the axial direction for fitting sealing elements such as seals or flanges which will therefore perform better both in terms of static or dynamic sealing and in terms of anchorage on one of the two rings. Lateral reserves of grease are increased.
Use may be made of a synthetic cage with a thicker heal, which allows higher speeds.
Use may be made of a synthetic cage in places where previously it was necessary to use a sheet metal cage with important advantages in terms of cost reduction, running noise reduction, rubbing torque reduction (less energy consumed, less heat generated), and increased grease life.
Specifically, it is known that the use of a plastic cage extends the life of the grease considerably, by a factor of the order of 2 to 3, by comparison with a steel cage depending on the load conditions and the application.
The zones of contact between the balls and the raceways are smaller, which leads to a reduction in the effects of churning/throttling of the grease, which also extends its life, reduces the torque and therefore the internal heating of the bearing, and its energy consumption.
The mass of the rotating parts is lowered because of the reduction in the diameter of the balls, which leads to a reduction in inertia, in gyroscopic effects, and in centrifugal forces.
In the electric motor applications, the outer ring is fixed and generally mounted in a light alloy housing, while the inner ring rotates and is mounted tightly on a rotating shaft.
In the context of this invention, the aforementioned advantages are enhanced by giving the outer ring a greater thickness at the bottom of the raceway than is the case for an outer ring of a conventional bearing of the ISO range. The pitch diameter Dm of the bearing, measured at the center of the balls, and therefore the peripheral speed of the balls at this pitch diameter is reduced, thus increasing the possibilities of raising the rotational speed of the rotating ring by comparison with a conventional bearing while at the same time reducing the running temperature.
The transmission of noise and vibration from the bearing to the housing of the outer ring is damped. The possibility of clamping the outer ring in its housing with lesser effects on the internal clearance of the bearing is increased. The detrimental effects that a housing with mediocre geometric properties has on the outer ring of the bearing are reduced.
Finally, the values of external size, outside diameter D, inside diameter d and width B of a bearing according to the invention are identical to those of a corresponding reference of conventional single row rigid ball bearings of the ISO range.
The bearings according to the invention are thus perfectly interchangeable with conventional bearings of the ISO range and afford a great many advantages.